This invention relates to color photothermographic imaging systems that utilize silver halide based radiation sensitive layers and associated formation of image dyes. In particular, this invention relates to such systems where at least one image dye is the reaction product of an image coupler and a thermally activated blocked developer in the presence of a phenolic compound.
Thermal solvents for use in photothermographic and thermographic systems are generally known. Heat processable photosensitive elements can be constructed so that after exposure, they can be processed in a substantially dry state by applying heat. Because of the much greater challenges involved in developing a dry or substantially dry color photothermographic system, however, most of the activity to date has been limited to black and white photothermographic systems, especially in the areas of health imaging and microfiche.
It is known how to develop latent image in a photographic element not containing silver halide wherein organic silver salts are used as a source of silver for image formation and amplification. Such processes are described in U.S. Pat. No. 3,429,706 (Shepard et al.) and U.S. Pat. No. 3,442,682 (Fukawa et al.). Dry processing thermographic systems are described in U.S. Pat. No. 3,152,904 (Sorenson et al.) and U.S. Pat. No. 3,457,075 (Morgan and Shely). A variety of compounds have been proposed as xe2x80x9ccarriersxe2x80x9d or xe2x80x9cthermal solventsxe2x80x9d or xe2x80x9cheat solventsxe2x80x9d for such systems, whereby these additives serve as solvents for incorporated developing agents, or otherwise facilitate the resulting development or silver diffusion processes. Acid amides and carbamates have been proposed as such thermal solvents by Henn and Miller (U.S. Pat. No. 3,347,675) and by Yudelson (U.S. Pat. No. 3,438,776). Bojara and de Mauriac (U.S. Pat. No. 3,667,959) disclose the use of non-aqueous polar solvents containing thione, xe2x80x94SO2xe2x80x94 and xe2x80x94COxe2x80x94 groups as thermal solvents and carriers in such photographic elements. Similarly, La Rossa (U.S. Pat. No. 4,168,980) discloses the use of imidazoline-2-thiones as processing addenda in heat developable photographic materials. Takahashi (U.S. Pat. No. 4,927,731) discloses a microencapsulated base activated heat developable photographic polymerization element containing silver halide, a reducing agent, a polymerizable compound, contained in a microcapsule and separate from a base or base precursor. In addition, a sulfonamide compound is included as a development accelerator.
Thermal solvents for use in substantially dry color photothermographic systems have been disclosed by Komamura et al. (U.S. Pat. No. 4,770,981), Komamura (U.S. Pat. No. 4,948,698), Aomo and Nakamaura (U.S. Pat. No. 4,952,479), and Ohbayashi et al. (U.S. Pat. No. 4,983,502). The terms xe2x80x9cheat solventxe2x80x9d and xe2x80x9cthermal solventxe2x80x9d in these disclosures refer to a substantially non-hydrolyzable organic material which is a liquid at ambient temperature or a solid at an ambient temperature but mixes (dissolves or melts or both) with other components at a temperature of heat treatment or below but higher than 40xc2x0 C., preferably above 50xc2x0 C. Such solvents may also be solids at temperatures above the thermal processing temperature. Their preferred examples include compounds which can act as a solvent for the developing agent and compounds having a high dielectric constant which accelerate physical development of silver salts. Alkyl and aryl amides are disclosed as xe2x80x9cheat solventsxe2x80x9d by Komamura et al. (U.S. Pat. No. 4,770,981), and a variety of benzamides have been disclosed as xe2x80x9cheat solventsxe2x80x9d by Ohbayashi et al. (U.S. Pat. No. 4,983,502). Polyglycols, derivatives of polyethylene oxides, beeswax, monostearin, high dielectric constant compounds having an xe2x80x94SO2xe2x80x94 or xe2x80x94COxe2x80x94 group such as acetamide, ethylcarbamate, urea, methylsulfonamide, polar substances described in U.S. Pat. No. 3,667,959, lactone of 4-hydroxybutanoic acid, methyl anisate, and related compounds are disclosed as thermal solvents in such systems. The role of thermal solvents in these systems is not clear, but it is believed that such thermal solvents promote the diffusion of reactants at the time of thermal development. Masukawa and Koshizuka disclose (in U.S. Pat. No. 4,584,267) the use of similar components (such as methyl anisate) as xe2x80x9cheat fusersxe2x80x9d in thermally developable light-sensitive materials. Baxendale and Wood in the Defensive Publication corresponding to U.S. application Ser. No. 825,478 filed Mar. 17, 1969 disclose water soluble lower-alkyl hydroxybenzoates as preprocessing stabilizers in silver salt heat-developable photographic elements.
U.S. Pat. No. 5,352,561 to Bailey et al. discloses the use of phenolic compounds (hydroxybenzene derivatives) for forming an improved dye image in an aqueous developable photographic dry dye-diffusion transfer element. A color coupler forms or releases a heat-transferable dye upon reaction of the coupler with the oxidation product of a primary amine developing agent. A dye receiving layer is placed in physical contact with the dye-diffusion transfer element and then combination heated to effect dye-diffusion.
Phenolic compounds are also disclosed for use in non-photothermographic systems. Okonogi et al. (U.S. Pat. No. 4,228,235) disclose 2,6-dialkyl hydroxybenzoates as dye light-fade stabilizers in an integral photographic, or non-diffusion transfer type, element. Hirano et al. (U.S. Pat. No. 4,474,874) disclose 5-substituted pyrogallols with amide, acyl, sulfone, or sulfate groups as color fog preventative agents (interlayer scavengers) in an integral photographic element or in an aqueous alkali color image transfer element Takahashi et al. (U.S. Pat. No. 5,169,742) disclose phenols with sulfone, amide and ester substituents as interlayer scavengers in an integral photographic element. Waki et al. (U.S. Pat. No. 4,626,494) describes an aqueous alkali activated image transfer element containing coupler solvents including 2-ethylhexyl hydroxybenzoate. Takahashi et al. (European Patent Application No. 276,319) disclose image generating layers incorporating low levels of hydroxybenzoates, salicylates and o-hydroxybenzophenones as dye light-stabilizers. Thirtle and Weissberger (U.S. Pat. No. 2,835,579) disclose aqueous processable color photographic elements that contain 2,4-di-n-alkyl-, 2-n-alkyl4-n-alkylacyl or 2-n-alkylacyl-4-n-alkylphenols as solvents for dye forming couplers. Sakai et al. (U.S. Pat. No. 4,774,166) disclose seven classes of materials, including as members of one class, arylsulfonylphenols, arylsulfamoylphenols and arylacylphenols as coupling-activity enhancing compounds employed in development processes not containing benzyl alcohol. Ishikawa and Sato (Japanese Kokai No. 62-25754) disclose hydroxybenzoates and salicylates as coupling-activity enhancing compounds in color photographic elements. Kimura et al. (U.S. Pat. No. 4,551,422) disclose the incorporation of substituted phenols, including alkylphenols, hydroxybenzoates and acylphenols in color photographic elements as hue shifting addenda.
It is an object of the present invention to provide an improved thermal solvent for photothermographic color elements. There is a need for a thermal solvent, in a photothermographic imaging element, that allows a blocked developing agent to be stable until development yet promotes rapid color development once processing has been initiated by heating the element and/or by applying a small amount of processing solution in a substantially dry environment, such as a solution of a base or acid or pure water held in a laminate for contact with the photothermographic element. A color photothermographic element that could be thermally developed by a dry or substantially dry process would be highly desirable. The existence of such developer chemistry would allow for very rapidly processed films that can be processed simply and efficiently in low cost photoprocessing kiosks.
A major problem that remains in dry phototothermographic systems, wherein the dye images require the reaction of a blocked developer and a dye-forming coupler through substantially dry gelatin, is how to facilitate the speed and ease with which such dye images may be formed. These and other problems may be overcome by the practice of our invention.
An object of the present invention is to overcome the disadvantages of the prior processes and products relating to color photothermographic systems. A further object of the present invention is to provide improved image dye formation in color photothermographic elements. In particular, the invention provides a chromogenic photothermographic element comprising radiation sensitive silver halide, a blocked developing agent, at least one coupler that forms an image dye upon reaction of said compound with the oxidation product of the unblocked developing agent, a hydrophilic binder, and a thermal solvent for facilitating dye image formation wherein said thermal solvent is a phenol or derivatives thereof that are essentially or substantially non-hydrolyzable and, when in the photographic element, soluble in the hydrophilic binder at ambient temperature or a solid at an ambient temperature but mixes (dissolves or melts or both) with other components, especially the blocked developer and coupler, at the temperature of heat treatment or below, but higher than 40xc2x0 C. and preferably above 50xc2x0 C.
The color photothermographic element comprises a blocked developer that decomposes (i.e., unblocks) on thermal activation to release a developing agent, wherein thermal activation is at a temperature of at least 60xc2x0 C., preferably at least 80xc2x0 C., more preferably at least 100xc2x0 C. In dry processing embodiments, thermal activation preferably occurs at temperatures between about 80 to 180xc2x0 C., preferably 100 to 160xc2x0 C. In not completely dry development (xe2x80x9csubstantially dryxe2x80x9d) systems, thermal activation preferably occurs at temperatures between about 60 and 140xc2x0 C. in the presence of added acid, base and/or water. In one preferred embodiment of the invention, the photothermographic element comprises an effective amount of a thermal solvent. In another preferred embodiment of the invention, the photothermographic element comprises a mixture of organic silver salts (inclusive of complexes) at least one of which is a silver donor, in order to reduce the amount of fog during thermal development.
The invention additionally relates to a method of image formation having the steps of: thermally developing an imagewise exposed photographic element having a blocked developer in association with a phenolic thermal solvent that decomposes on thermal activation to release a developing agent that reacts with a coupler to form a developed image. In one embodiment of the invention, a positive image can be formed by scanning the developed image to form a first electronic image representation (or xe2x80x9celectronic recordxe2x80x9d) from said developed image, digitizing said first electronic record to form a digital image, modifying said digital image to form a second electronic image representation, and storing, transmitting, printing or displaying said second electronic image representation.
The invention further relates to a one-time use camera having a light sensitive photographic element comprising a support and a blocked developer that decomposes to release a photographically useful group on thermal activation. The invention further relates to a method of image formation having the steps of imagewise exposing such a light sensitive photographic element in a one-time-use camera having a heater and thermally processing the exposed element in the camera.